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In many cases, it is not sufficient to eliminate the PDL influence from the insertion-loss result. Instead, the PDL is considered as a separate characteristic and must be measured in addition to the insertion loss. The two most important PDL-measurement techniques are polarization scanning and the Mueller method. Both methods are explained in detail below.   >> Polarization Scanning Method The figure below shows the principle measurement setup for polarization scanning. This measurement is usually based on the fact that laser sources produce nearly 100% polarized light. The polarization controller has to convert the fixed input polarization state to all

>> The Optical Time Domain Reflectometer (OTDR) OTDR is connected to one end of any fiber optic system up to 250km in length. Within a few seconds, we are able to measure the overall loss, or the loss of any part of a system, the overall length of the fiber and the distance between any points of interest. OTDR is a amazing test instrument for fiber optic systems. 1. A Use for Rayleigh Scatter As light travels along the fiber, a small proportion of it is lost by Rayleigh scattering. As the light is scattered in all directions, some of

>> The Protocol Stacks The classic 7 layers OSI model view of networks needs some embellishment to handle the variety of networks and protocols that are proliferating today. A more realistic layered model for today’s networks would employ multiple protocol stacks residing one on top of the other. Each stack incorporates several sublayers, which may provide functions resembling traditional physical, data link, and network layers. Let’s consider the IP over Ethernet network shown in the following figure. In this case, the IP network treats the SONET network as providing it with point-to-point links between IP routers. The SONET layer itself,

>> The Advantages of Optical Networks 1. Flexible Bandwidth Delivery In addition to providing enormous capacities in the network, an optical network provides a common infrastructure over which a variety of services can be delivered. These optical networks are also increasingly becoming capable of delivering bandwidth in a flexible manner where and when needed. 2. High Capacity and Immune to EMI and RFI Optical fiber offers much higher bandwidth than copper cables and is less susceptible to various kinds of electromagnetic interferences and other undesirable effects. As a result, it is the preferred medium for transmission of data at anything

>> What Is a Virtual LAN (VLAN)? A LAN is a local area network and is defined as all devices in the same broadcast domain. Here is a typical LAN structure. In the above LAN configuration, the LAN is composed of hierarchical hubs, each workgroup can be physically separated from all the other workgroups. However, this is not always possible. Consider this example. A college staff belongs to the HR department and her compute is attached to the HR Department LAN. But she is also responsible for managing the accounts relating to research grants, general teaching and research funding. In